Iyov on the rules for Jews(If you click, don't scroll all the way down unless you can stand graphic pictures of the dead):
I think that the Jewish law is quite clear on this point -- despite what the New York Times says, for observant Jews, voluntary tattoos are clearly forbidden.
Then he points out how tattoos were used in the Holocaust and puts up the pictorial proof.
I have an idea that tattoos have become so acceptable because we are living in a sort of reverse discrimination age, where to many people's minds, the low class are the class to celebrate. What surprises me though, is how many Christians are so easy with tattoos. God made unclean foods clean in the New Testament, but point to me where he did that for tattoos. I'm sure a man who has tattoos can convert and become Christian, but why should a Christian get a tattoo?
It seems to me to indicate that one's thought process is very much NOT where it should be.
I did find some explanation as to why there is no direct prohibition by the Catholic Church. At CUF.org. It seems the freedom for a Catholic to do so is framed by cultural considerations. Frankly, I don't think very many people are paying attention to this, because it sounds like anyone honestly assessing this the way they suggest one should wouldn't get a tattoo in the United States. Oh sure, I could think up some highly specialized reasons one would do so, but they don't usually apply to middle class Christians.